1. Field of the Invention
The present invention relates to a head tracking system in a disk drive and, more particularly, to a head tracking system for an optical head having a focusing lens irradiating an optical spot to a disk file.
2. Description of the Related Art
An optical disk drive system is proposed which has two stages of actuators for positioning of an optical spot, including a first actuator or lens actuator for driving a focusing lens relative to an optical head and a second actuator or a voice coil motor for driving the optical head relative to the optical disk file, both in a radial direction of the optical disk file. The optical disk drive system of this type is described in, for example, Patent Publication No. JP-A-61(1986)-177641. The tracking system described in the publication provides a high-speed seeking as well as an accurate positioning of the optical spot.
The head tracking system in the optical disk drive system as mentioned above carries the optical spot to a target track indicated by the disk drive system while controlling the radial speed of the focusing lens to follow a normalized speed profile during seeking period of the optical spot. An example of the normalized speed profile includes a first profile section in which the speed of the optical spot is increased with a constant acceleration and a second profile section in which the speed of the optical spot is decreased with a constant deceleration.
During the seeking operation, the head tracking system controls the lens actuator to move the focusing lens in accordance with the normalized speed profile and detects a position error of the focusing lens relative to the reference position of the optical head in the radial direction of the optical disk. The head tracking system then drives the voice coil motor and controls the lens actuator so that the position error of the focusing lens relative to the reference position becomes zero.
The normalized speed profile should be determined based on the seek stroke between the target track and the present track before seeking and the maximum output of the voice coil motor to provide a sufficient margin of the lens speed even in the case of inclination of the optical head, vibration of the focusing lens and fluctuation of the supply voltage.